The present invention relates generally to radio transceivers operative in a cellular, communication system, and, more particularly, to a radio transceiver, and associated method therefor, having a fixed calling capacity.
A communication system is operative to transmit information (referred to hereinbelow as an "information signal") between two or more locations, and includes, at a minimum, a trasmitter and a receiver interconnected by a communication channel. A radio communication system is a communication system in which the transmission channel comprises a radio-frequency channel wherein the radio-frequency channel is defined by a range of frequencies of the communication spectrum.
The transmitter, which forms a portion of a radio communication system, includes circuitry for converting the information signal into a form suitable for transmission thereof upon a radio-frequency channel. Such circuitry includes modulation circuitry which performs a process referred to as modulation. In such a process, the information signal which is to be transmitted is impressed upon a radio-frequency electromagnetic wave.
The radio-frequency electromagnetic wave upon which the information signal is impressed is of a frequency within a range of frequencies defining in the radio-frequency channel upon which the information is to be transmitted. The radio-frequency, electromagnetic wave is commonly referred to as a "carrier signal," and the radio-frequency, electromagnetic wave, once modulated by the information signal, is commonly referred to as a modulated signal.
Various modulation schemes are known for impressing the information signal upon the carrier signal to form thereby the modulated signal. For instance, amplitude modulation, frequency modulation, phase modulation, and combinations thereof are all modulation schemes by which an information signal may be impressed upon a carrier wave to form a modulated signal.
Radio communication systems are advantageous in that no physical interconnection is required between the transmitter and the receiver; once the information signal is modulated to form a modulated signal, the modulated signal may be transmitted over large distances.
A two-way, radio communication system is a radio communication system, similar to the radio communication system described above, but which further permits both transmission of information to a remote location and reception of information transmitted by a transmitter located at the remote location. Each location of such two-way, radio communication system contains both a transmitter and a receiver. The transmitter and receiver positioned at a single location typically comprise a unit referred to as a radio transceiver, or, more simply, a transceiver.
A cellular, communication system is one type of radio communication system. Radio transceivers (conventionally referred to as radiotelephones or cellular phones) operative in such a cellular, communication system contain circuitry permitting simultaneous generation and reception of modulated signals. Two-way communication between a radiotelephone and remotely-located transceivers is thereby permitted. The remotely-located transceivers, referred to as "base stations", are physically connected to a conventional telephonic network to permit communication between a radiotelephone and a fixed site of a conventional, telephonic network. (A fixed site of the conventional, telephonic network may also, of course, comprise a base station capable of transmitting modulated signals to a radio transceiver --thereby permitting communication between two radio transceivers.) A cellular, communication system is formed by positioning numerous base stations at spaced-apart locations throughout a geographical area. Each base station contains circuitry to receive modulated signal transmitted thereto by one, or many, radiotelephones.
A frequency band of the electromagnetic frequency spectrum (in the United States extending between 800 megahertz and 900 megahertz) is allocated for radiotelephone communication upon a cellular, communication system. The allocated frequency band is further divided into a plurality of transmission channels of defined bandwidths. Modulated signals generated by radiotelephones are transmitted upon selected ones of the transmission channels defined thereon. Similarly, modulated signals generated by the base stations are also transmitted upon selected ones of the transmission channels defined upon such frequency band.
Radiotelephones operative in such a cellular, communication system have been designed to be of many types of constructions. Most of such radiotelephone construction may be classified as being of two general construction-types, namely, a construction-type generically referred to as a "mobile phone" and a construction type generically referred to as a "portable phone". (A third construction-type, generically referred to as a "transportable phone", has many of the characteristics of a portable phone, and will be considered hereinbelow as such.)
A mobile phone is designed to be mounted fixedly in a motor vehicle. A mobile phone is advantageous in that such a phone may be conveniently powered by the power supply of the motor vehicle in which the mobile phone is mounted. Additionally, because of such fixed positioning of the mobile phone in a motor vehicle, additional apparatus may be mounted in such motor vehicle to facilitate usage of such mobile phone by a user during operation of the motor vehicle. Of course, as such a mobile phone is typically fixedly mounted in such motor vehicle, portability of such a mobile phone is oftentimes limited.
A portable phone, conversely, is of reduced physical dimensions, thereby to permit convenient carriage of such a portable phone on the person of a user thereof. However, a portable power supply (typically a rechargeable battery) must be carried with the portable phone to permit operation of such phone. And, such portable power supply is of finite energy storage capacity which limits the operational period of the portable phone.
Use of a radiotelephone, of either construction-type, in a cellular, communication system permits the user to communicate telephonically without any fixed connection to a conventional telephonic network. Calls may be initiated by the user, or calls may be initiated by another, and received by the user made to the user, similar to telephonic communication in a conventional, wireline telephonic network. Use of such transceivers may for example, increase the productivity of a user, allowing the user to communicate telephonically during times when the user would otherwise be unable to communicate telephonically upon a conventional, wireline network (such as, e.g., when the user is operating a motor vehicle, waiting in an airport, etc.).
Use of such a radiotelephone in a cellular, communication system is perhaps of greatest benefit in the event of emergency, as such a radio transceiver may be used to report, for example, roadside breakdowns, emergency roadside conditions, or other emergency conditions. In essence, when used in such situations, the radiotelephone is operative as a security device.
Many potential users of a cellular, communication system would be eager to have available a radiotelephone for use as a security device, but not require a radiotelephone for other purposes.
If a radiotelephone is used solely as a security device, the radiotelephone would be actually operated only sporadically. Such minimal operation of the radiotelephone if used solely as a security device would result in a negligible increase in usage of a cellular, communication system.
Such usage of a cellular, communication system is commonly referred to as the "load" upon the system. The "loading" upon a cellular, communication system determines the number, and location, of base stations required to permit usage of the cellular, communication system by users desiring to communicate thereon at any given time. Because a radiotelephone operative only as a security device would be used only rarely, large numbers of users of such radiotelephones operative only as security devices would not result in significant increase in the "loading" of an existing, cellular, communication system. Accordingly, there would be little likelihood of an existing, cellular, communication system reaching, or exceeding, full capacity of usage thereof as a result of even very large increases in numbers of users of the cellular, communication system, if such additional users operate radiotelephones only as security devices.
Such users, however, could not be permitted to operate such radiotelephones except as security devices without increasing the "loading" of an existing, cellular, communication system.
What is needed, therefore, is a radiotelephone construction capable of use solely as a security device.